On Sat, 26 Aug 2006 09:39:46 GMT, Paul Hinman
wrote:

As long as gravity exists will it ever be possible to get a perfectly
horizontal dipole?

Hi Paul,

If you read my further responses to Owen, you find the discussion of
catenaries. In that regard, the answer to your question is
unquestionably YES!

You merely need to provide a catenary supporting the perfectly
horizontal dipole. Regard any suspension bridge to discover the
mechanics of construction. And, yes, the road bed is not horizontal,
but an arc built to anticipate load; the ingenious antenna builder can
reconcile this (trolley systems across the world with overhead
suspended wires solve this easily).

The question for this relative neophyte is,
what effect does the sag have on antenna performance?

Barring the suspension method, and the wire sags, it becomes a
question of how much, and more importantly, in what relation to
ground? If you have a 160M dipole with the ends up 10 meters, and a
sag of only 0.1°, then you still have a dog. If it is a 10M dipole
with a 10° sag, then you have a performer. This is a 100 fold
variation that would seem to invert expectations - if were not for the
wavelength and relation to ground.

73's
Richard Clark, KB7QHC

On Sat, 26 Aug 2006 09:39:46 GMT, Paul Hinman
wrote:


wire might not survive. The question for this relative neophyte is,
what effect does the sag have on antenna performance?

Yes, perhaps you got on the wrong tram in the discussion about sag. It
would be easy if you hadn't read the entire thread.

Low sag is obtained by high wire tension.

High wire tension under static conditions increases the risk of
breaking under wind loading.

Antennas that have broken don't perform so well.

Owen

PS: In answer to your question as to whether a dipole can ever be
perfectly horizontal, perhaps no, perfect is probably not achievable
by any real thing, but yes, it can be done to a close approximation,
but it is probably not practical in most situations. Think of an
electric railway with overhead power, the power conductor is very
close to constant grade and parallel to the tracks, think of
suspension bridges with an approximately flat roadway. There are of
course other solutions as well.

--

Apart from the challenge of making reliable connections to aluminium,
are there other "issues" that come to mind in using such wire for
antennas?

Owen
--



I've seen comments suggesting that steele core wire is not a good idea
if you live in any kind of humid climate..... the cover clad develops pin-
holes over time which allows moisture to start the rust process of the
inner steel core. Breakage soon follows..... The comments I received
were regarding copper clad, though. I don't know if aluminum would have
the same potential problem or not.


Ed K7AAT

COPPER-WELD

There are no issues of "reliable connections".

NOTE: Copper-weld is copper cladded steel wire. It's been used for years as a
very reliable antenna with long spans. Catenary stresses are carried by the
steel wire component.

/s/ DD

Owen Duffy wrote:

In searching the 'net for wire suitable for wire antennas, I came
across a single core 2.7mm diameter 40% aluminium clad high tensile
steel wire.

I am trying to get some further detail on its Guaranteed Breaking
Strength, but my guess is that the steel core is probably somewhere
about 1000 MPa UTS, and will give an overall GBS around 4kN.

The coating thickness looks like high conductivity aluminium, with a
thickness of 300 microns, which is 5 skin depths at 1.8MHz, so
conductivity should be good.

Apart from the challenge of making reliable connections to aluminium,
are there other "issues" that come to mind in using such wire for
antennas?

Owen
--